Method of polycarbonate preparation

ABSTRACT

Polycarbonates containing low or undetectable levels of Fries rearrangement product may be prepared by the melt reaction of a dihydroxy aromatic compound such as bisphenol A with an ester-substituted diaryl carbonate such as the diaryl carbonate of methyl salicylate, bis-methyl salicyl carbonate. Low levels of Fries product are obtained as the combined result of a highly effective catalyst system which suppresses the Fries reaction and the use of lower melt polymerization temperatures relative to temperatures required for the analogous polymerization reaction using diphenyl carbonate.

BACKGROUND OF THE INVENTION

[0001] This invention relates to the preparation of polycarbonates bythe melt reaction of a bisphenol with an ester-substituted diarylcarbonate. More particularly, the instant invention relates to theformation under mild conditions of polycarbonates having extremely lowlevels of Fries rearrangement products and possessing a high level ofendcapping.

[0002] Polycarbonates, such as bisphenol A polycarbonate, are typicallyprepared either by interfacial or melt polymerization methods. Thereaction of a bisphenol such as bisphenol A (BPA) with phosgene in thepresence of water, a solvent such as methylene chloride, an acidacceptor such as sodium hydroxide and a phase transfer catalyst such astriethylamine is typical of the interfacial methodology. The reaction ofbisphenol A with a source of carbonate units such as diphenyl carbonateat high temperature in the presence of a catalyst such as sodiumhydroxide is typical of currently employed melt polymerization methods.Each method is practiced on a large scale commercially and each presentssignificant drawbacks.

[0003] The interfacial method for making polycarbonate has severalinherent disadvantages. First it is a disadvantage to operate a processwhich requires phosgene as a reactant due to obvious safety concerns.Second it is a disadvantage to operate a process which requires usinglarge amounts of an organic solvent because expensive precautions mustbe taken to guard against any adverse environmental impact. Third, theinterfacial method requires a relatively large amount of equipment andcapital investment. Fourth, the polycarbonate produced by theinterfacial process is prone to having inconsistent color, higher levelsof particulates, and higher chloride content, which can cause corrosion.

[0004] The melt method, although obviating the need for phosgene or asolvent such as methylene chloride requires high temperatures andrelatively long reaction times. As a result, by-products may be formedat high temperature, such as the products arising by Fries rearrangementof carbonate units along the growing V polymer chains. Friesrearrangement gives rise to undesired and uncontrolled polymer branchingwhich may negatively impact the polymer's flow properties andperformance.

[0005] Some years ago, it was reported in U.S. Pat. No. 4,323,668 thatpolycarbonate could be formed under relatively mild conditions byreacting a bisphenol such as BPA with the diaryl carbonate formed byreaction phosgene with methyl salicylate. The method used relativelyhigh levels of transesterification catalysts such as lithium stearate inorder to achieve high molecular weight polycarbonate. High catalystloadings are particularly undesirable in melt polycarbonate reactionssince the catalyst remains in the product polycarbonate following thereaction. The presence of a transesterification catalyst in a thepolycarbonate may shorten the useful life span of articles madetherefrom by promoting increased water absorption, polymer degradationat high temperatures and discoloration.

[0006] It would be desirable, therefore, to minimize the amount ofcatalyst required in the for the melt preparation of polycarbonate frombisphenols and ester substituted diaryl carbonates such as bis-methylsalicyl carbonate.

BRIEF SUMMARY OF THE INVENTION

[0007] The present invention provides a method for preparingpolycarbonate comprising heating a mixture comprising a catalyst, atleast one diaryl carbonate having structure I

[0008] wherein R¹ and R² are independently C₁-C₂₀ alkyl radicals, C₄-C₂₀cycloalkyl radicals or C₄-C₂₀ aromatic radicals, R³ and R⁴ areindependently at each occurrence a halogen atom, cyano group, nitrogroup, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, C₄-C₂₀ aromaticradical, C₁-C₂₀ alkoxy radical, C₄-C₂₀ cycloalkoxy radical, C₄-C₂₀aryloxy radical, C₁ - C₂₀ alkylthio radical, C₄-C₂₀ cycloalkylthioradical, C₄-C₂₀ arylthio radical, C₁-C₂₀ alkylsulfinyl radical, C₄-C₂₀cycloalkylsulfinyl radical, C₄-C₂₀ arylsulfinyl radical, C₁-C₂₀alkylsulfonyl radical, C₄-C₂₀ cycloalkylsulfonyl radical, C₄-C₂₀arylsulfonyl radical, C₁-C₂₀ alkoxycarbonyl radical, C₄-C₂₀cycloalkoxycarbonyl radical, C₄-C₂₀ aryloxycarbonyl radical, C₂-C₆₀alkylamino radical, C₆-C₆₀ cycloalkylamino radical, C₅-C₆₀ arylaminoradical, C₁-C₄₀ alkylaminocarbonyl radical, C₄-C₄₀cycloalkylaminocarbonyl radical, C₄-C₄₀ arylaminocarbonyl radical, andC₁-C₂₀ acylamino radical; and b and c are independently integers 0-4;and at least one dihydroxy aromatic compound, said catalyst comprisingat least one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compoundor a mixture thereof, said source of alkaline earth ions or alkali metalions being present in an amount such that between about 10⁻⁵ and about10⁻⁸ moles of alkaline earth metal ions or alkali metal ions are presentin the mixture relative per mole of dihydroxy aromatic compoundemployed, said quaternary ammonium compound, quaternary phosphoniumcompound or mixture thereof being present in an amount between about2.5×10⁻³ and about 1×10⁻⁶ moles per mole of dihydroxy aromatic compoundemployed.

[0009] The present invention further relates to a method for formingpolycarbonates by reaction of an ester-substituted diaryl carbonate inwhich the level of Fries rearrangement product in the productpolycarbonate is less than about 1000 parts per million (ppm) and thelevel of internal ester carbonate linkages in the product polycarbonateis less than about 1 percent of the total number of moles of dihydroxyaromatic compound employed and the level of terminal hydroxy estergroups in the product polycarbonate is less than about 1 percent of thetotal number of moles of dihydroxy aromatic compound employed.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention may be understood more readily by referenceto the following detailed description of preferred embodiments of theinvention and the examples included therein. In the followingspecification and the claims which follow, reference will be made to anumber of terms which shall be defined to have the following meanings:

[0011] The singular forms “a”, “an” and “the” include plural referentsunless the context clearly dictates otherwise.

[0012] “Optional” or “optionally” means that the subsequently describedevent or circumstance may or may not occur, and that the descriptionincludes instances where the event occurs and instances where it doesnot.

[0013] As used herein the term “polycarbonate” refers to polycarbonatesincorporating structural units derived from one or more dihydroxyaromatic compounds and includes copolycarbonates and polyestercarbonates.

[0014] As used herein, the term “melt polycarbonate” refers to apolycarbonate made by the transesterification of a diaryl carbonate witha dihydroxy aromatic compound.

[0015] “BPA” is herein defined as bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

[0016] “Catalyst system” as used herein refers to the catalyst orcatalysts that catalyze the transesterification of the bisphenol withthe diaryl carbonate in the melt process.

[0017] The terms “bisphenol”, “diphenol” and “dihydric phenol” as usedherein are synonymous.

[0018] “Catalytically effective amount” refers to the amount of thecatalyst at which catalytic performance is exhibited.

[0019] As used herein the term “Fries product” is defined as astructural unit of the product polycarbonate which upon hydrolysis ofthe product polycarbonate affords a carboxy-substituted dihydroxyaromatic compound bearing a carboxy group adjacent to one or both of thehydroxy groups of said carboxy-substituted dihydroxy aromatic compound.For example, in bisphenol A polycarbonate prepared by a melt reactionmethod in which Fries reaction occurs, among the Fries products withinthe product polycarbonate are those structural units, for examplestructure VIII below, which afford 2-carboxy bisphenol A upon completehydrolysis of the product polycarbonate.

[0020] The terms “Fries product” and “Fries group” are usedinterchangeably herein.

[0021] The terms “Fries reaction” and “Fries rearrangement” are usedinterchangeably herein.

[0022] As used herein the term “aliphatic radical” refers to a radicalhaving a valence of at least one comprising a linear or branched arrayof atoms which is not cyclic. The array may include heteroatoms such asnitrogen, sulfur and oxygen or may be composed exclusively of carbon andhydrogen. Examples of aliphatic radicals include methyl, methylene,ethyl, ethylene, hexyl, hexamethylene and the like.

[0023] As used herein the term “aromatic radical” refers to a radicalhaving a valence of at least one comprising at least one aromatic group.Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl,naphthyl, phenylene, and biphenyl. The term includes groups containingboth aromatic and aliphatic components, for example a benzyl group.

[0024] As used herein the term “cycloaliphatic radical” refers to aradical having a valance of at least one comprising an array of atomswhich is cyclic but which is not aromatic. The array may includeheteroatoms such as nitrogen, sulfur and oxygen or may be composedexclusively of carbon and hydrogen. Examples of cycloaliphatic radicalsinclude cyclcopropyl, cyclopentyl cyclohexyl, tetrahydrofuranyl and thelike.

[0025] In the present invention it has been discovered that extremelylow levels of catalyst may be employed to prepare polycarbonate usingthe melt reaction of an ester substituted diaryl carbonate with abisphenol. The use of very low catalyst loadings is desirable from atleast two perspectives. First, the use of low catalyst levels duringmelt polymerization tends to suppress the formation of undesired Friesrearrangement products. Second, because residual catalyst present in thepolymer tends to decrease the useful life span of articles made from itby increasing water absorption, decreasing thermal stability andpromoting discoloration, its minimization is desirable. Thepolycarbonate prepared by the method of the present invention is freeof, or contains undetectable levels of Fries rearrangement products.Moreover, in the absence of an added exogenous monofunctional phenol theproduct polycarbonate is very highly endcapped with less than 50% of theendgroups being free hydroxyl groups. Where an exogenous monofunctionalphenol is added to the polymerization mixture, high levels ofincorporation of said phenol are observed. In this manner both theidentity of the polymer endgroups and the polymer molecular weight maybe controlled in the melt reaction.

[0026] In the process of the present invention an ester-substituteddiaryl carbonate having structure I is reacted under melt reactionconditions with at least one dihydroxy aromatic compound in the presenceof at least one source of alkaline earth ions or alkali metal ions, andan organic ammonium compound or an organic phosphonium compound or acombination thereof. Ester-substituted diaryl carbonates I areexemplified by bis-methyl salicyl carbonate (CAS Registry No.82091-12-1), bis-ethyl salicyl carbonate, bis-propyl salicyl carbonate,bis-butyl salicyl carbonate, bis-benzyl salicyl carbonate, bis-methyl4-chlorosalicyl carbonate and the like. Typically bis-methyl salicylcarbonate is preferred.

[0027] The dihydroxy aromatic compounds of the present invention areselected from the group consisting of bisphenols having structure II,

[0028] wherein R⁵-R¹² are independently a hydrogen atom, halogen atom,nitro group, cyano group, C₁₋C₂₀ alkyl radical C₄₋C₂₀ cycloalkylradical, or C₆₋C₂₀ aryl radical; W is a bond, an oxygen atom, a sulfuratom, a SO₂ group, a C₆-C₂₀ aromatic radical, a C₆-C₂₀ cycloaliphaticradical or the group

[0029] wherein R¹³ and R ¹⁴ are independently a hydrogen atom, C₁₋C₂₀alkyl radical, C₄₋C₂₀ cycloalkyl radical, or C₄₋C₂₀ aryl radical; or R¹³and R¹⁴ together form a C₄₋C₂₀ cycloaliphatic ring which is optionallysubstituted by one or more C₁₋C₂₀ alkyl, C₆₋C₂₀ aryl, C₅₋C₂₁ aralkyl,C₅₋C₂₀ cycloalkyl groups or a combination thereof; dihydroxy benzeneshaving structure III

[0030] wherein R¹⁵ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁₋C₂₀ alkyl radical, C₄₋C₂₀cycloalkyl radical C₄₋C₂0 aryl radical, and d is an integer from 0 to 4;and dihydroxy naphthalenes having structures IV and V

[0031] wherein R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently at eachoccurrence a hydrogen atom, halogen atom, nitro group, cyano group,C₁₋C₂₀ alkyl radical, C₄₋C₂₀ cycloalkyl radical C₄₋C₂₀ aryl radical; eand f are integers of from 0 to 3, g is an integer from 0 to 4, and h isan integer from 0 to 2.

[0032] Suitable bisphenols II are illustrated by2,2-bis(4-hydroxyphenyl)-propane (bisphenol A);2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(3-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-phenyl-4-hydroxyphenyl)propane; 2,2-bis(3,5-dichloro-4-hydroxyphenyl)-propane;2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane;2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-disopropyl-4-hydroxy-phenyl)propane;2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3,5-diphenyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-propane;2,2-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)propane;2,2-bis(2,6-dichloro-3,5-dimethyl-4-hydroxy-phenyl)propane;2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)cyclobexane;1,1-bis(4-hydroxy-3-methylphenyl)-cyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dibromo-4-hydroxy-phenyl)cyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-5-phenyl-4-hydroxyphenyl)cyclo-hexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-cyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)cyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclo-hexane;1,1-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane; 1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;4,4′dihydroxy-1,1-biphenyl; 4,4′-dihydroxy-3, 3,′-dimethyl-1,1-biphenyl;4,4′-dihydroxy-3,3′-dioctyl-1,1-biphenyl; 4,4′-dihydroxydiphenylether;4,4′-dihydroxydiphen ylthioether;1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene;1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene;1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene and1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene.

[0033] Suitable dihydroxy benzenes III are illustrated by hydroquinone,resorcinol, methylhydroquinone, phenylhydroquinone, 4-phenylresorcinoland 4-methylresorcinol.

[0034] Suitable dihydroxy naphthalenes IV are illustrated by2,6-dihydroxy naphthalene; 2,6-dihydroxy-3-methyl naphthalene; and2,6-dihydroxy-3-phenyl naphthalene.

[0035] Suitable dihydroxy naphthalenes V are illustrated by1,4-dihydroxy naphthalene; 1,4-dihydroxy-2-methyl naphthalene;1,4-dihydroxy-2-phenyl naphthalene and 1,3-dihydroxy naphthalene.

[0036] The catalyst used in the method of the present inventioncomprises at least one source of alkaline earth ions or alkali metalions, and at least one quaternary ammonium compound, quaternaryphosphonium compound or a mixture thereof, said source of alkaline earthions or alkali metal ions being used in an amount such that the amountof alkaline earth or alkali metal ions present in the reaction mixtureis in a range between about 10⁻⁵ and about 10⁻⁸ moles alkaline earth oralkali metal ion per mole of dihydroxy aromatic compound employed.

[0037] The quaternary ammonium compound is selected from the group oforganic ammonium compounds having structure VI

[0038] wherein R²⁰-R²³ are independently a C₁₋C₂₀ alkyl radical, C₄₋C₂₀cycloalkyl radical or a C₄₋C₂₀ aryl radical and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isselected from the group consisting of hydroxide, halide, carboxylate,sulfonate, sulfate, formate, carbonate, and bicarbonate.

[0039] Suitable organic ammonium compounds comprising structure VI areillustrated by tetramethyl ammonium hydroxide, tetrabutyl ammoniumhydroxide, tetramethyl ammonium acetate, tetramethyl ammonium formateand tetrabutyl ammonium acetate.

[0040] The quaternary phosphonium compound is selected from the group oforganic phosphonium compounds having structure VII

[0041] wherein R²⁴-R²⁷ are independently a C₁₋C₂₀ alkyl radical, C₄₋C₂₀cycloalkyl radical or a C₄₋C₂₀ aryl radical and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isan anion selected from the group consisting of hydroxide, halide,carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate.[0001] Suitable organic phosphonium compounds comprising structure VIIare illustrated by tetramethyl phosphonium hydroxide, tetramethylphosphonium acetate, tetramethyl phosphonium formate, tetrabutylphosphonium hydroxide, and tetrabutyl phosphonium acetate.

[0042] Where X⁻ is a polyvalent anion such as carbonate or sulfate it isunderstood that the positive and negative charges in structures VI andVII are properly balanced. For example, where R²⁰ -R²³ in structure VIare each methyl groups and X⁻ is carbonate, it is understood that X⁻represents ½ (CO₃ ⁻²).

[0043] Suitable sources of alkaline earth ions include alkaline earthhydroxides such as magnesium hydroxide and calcium hydroxide. Suitablesources of alkali metal ions include the alkali metal hydroxidesillustrated by lithium hydroxide, sodium hydroxide and potassiumhydroxide. Other sources of alkaline earth and alkali metal ions includesalts of carboxylic acids, such as sodium acetate and derivatives ofethylene diamine tetraacetic acid (EDTA) such as EDTA tetrasodium salt,and EDTA magnesium disodium salt.

[0044] In the method of the present invention an ester-substituteddiaryl carbonate I, at least one dihydroxy aromatic compound and acatalyst are contacted in a reactor suitable for conducting meltpolymerization. The relative amounts of ester-substituted diarylcarbonate and dihydroxy aromatic compound are such that the molar ratioof carbonate I to dihydroxy aromatic compound is in a range betweenabout 1.20 and about 0.8, preferably between about 1.10 and about 0.9and still more preferably between about 1.05 and about 1.01.

[0045] The amount of catalyst employed is such that the amount ofalkaline earth metal ion or alkali metal ions present in the reactionmixture is in a range between about 1×10⁻⁵ and about 1×10⁻⁸, preferablybetween about 5×10⁻⁵ and about 1×10⁻⁷, and still more preferably betweenabout 5×10⁻⁵ and about 5×10⁻⁷ moles of alkaline earth metal ion oralkali metal ion per mole dihydroxy aromatic compound employed. Thequaternary ammonium compound, quaternary phosphonium compound or amixture thereof is used in an amount corresponding to about 2.5×10⁻³ and1×10⁻⁶ moles per mole dihydroxy aromatic compound employed.

[0046] Typically the ester-substituted diaryl carbonate, at least onedihydroxy aromatic compound and the catalyst are combined in a reactorwhich has been treated to remove adventitious contaminants capable ofcatalyzing both the transesterification and Fries reactions observed inuncontrolled melt polymerizations of diaryl carbonates with dihydroxyaromatic compounds. Contaminants such as sodium ion adhering to thewalls of a glass lined reactor are typical and may be removed by soakingthe reactor in mild acid, for example 3 normal hydrochloric acid,followed by removal of the acid and soaking the reactor in high puritywater, such as deionized water.

[0047] In one embodiment of the present invention an ester-substituteddiaryl carbonate, such as bis-methyl salicyl carbonate, at least onedihydroxy aromatic compound, such as BPA, and a catalyst comprisingalkali metal ions, such as sodium hydroxide, and a quaternary ammoniumcompound, such as tetramethyl ammonium hydroxide, or a quaternaryphosphonium compound, such as tetrabutyl phosphonium acetate, arecharged to a reactor and the reactor is purged with an inert gas such asnitrogen or helium. The reactor is then heated to a temperature in arange between about 100° C. and about 340° C., preferably between about100° C. and about 280° C., and still more preferably between about 140°C. and about 240° C. for a period of from about 0.25 to about 5 hours,preferably from about 0.25 to about 2 hours, and still more preferablyfrom about 0.25 hours to about 1.25 hours. While the reaction mixture isheated the pressure over the reaction mixture is gradually reduced fromambient pressure to a final pressure in a range between about 0.001 mmHgand about 400 mmHg, preferably 0.01 mmHg and about 100 mmHg, and stillmore preferably about 0.1 mmHg and about 10 mmHg.

[0048] Control of the pressure over the reaction mixture allows theorderly removal of the phenolic by-product formed when the dihydroxyaromatic compound undergoes a transesterification reaction with aspecies capable of releasing a phenolic by-product, for examplebis-methyl salicyl carbonate or a growing polymer chain endcapped by amethyl salicyl group. As noted above the reaction may be conducted atsubambient pressure. In an alternate embodiment of the present inventionthe reaction may be conducted at slightly elevated pressure, for examplea pressure in a range between about 1 and about 2 atmospheres.

[0049] As noted, the use of excessive amounts of catalyst may affectnegatively the structure and properties of a polycarbonate preparedunder melt polymerization conditions. The present invention provides amethod of melt polymerization employing a highly effective catalystsystem comprising at least one source of alkaline earth or alkali metalions, and a quaternary ammonium compound or quaternary phosphoniumcompound or mixture thereof which provides useful reaction rates at verylow catalyst concentrations, thereby minimizing the amount of residualcatalyst remaining in the product polycarbonate. Limiting the amount ofcatalyst employed according to the method of the present inventionprovides a new and useful means of controlling the structural integrityof the product polycarbonate as well. Thus, the method of the presentinvention provides a product polycarbonate having a weight averagemolecular weight, as determined by gel permeation chromatography, in arange between about 10,000 and about 100,000 Daltons, preferably betweenabout 15,000 and about 60,000 Daltons, and still more preferably betweenabout 15,000 and about 50,000 Daltons said product polycarbonate havingless than about 1000, preferably less than about 500, and still morepreferably less than about 100 parts per million (ppm) Fries product.Structure VIII below

[0050] illustates the Fries product structure present in a polycarbonateprepared from bisphenol A. As indicated, the Fries product may serve asa site for polymer branching, the wavy lines indicating polymer chainstructure.

[0051] In addition to providing a product polycarbonate containing onlyvery low levels of Fries products, the method of the present inventionprovides polycarbonates containing very low levels of other undesirablestructural features which arise from side reactions taking place duringmelt the polymerization reaction between ester-substituted diarylcarbonates I and dihydroxy aromatic compounds. One such undesirablestructural feature has structure IX

[0052] and is termed an internal ester-carbonate linkage. Structure IXis thought to arise by reaction of an ester-substituted phenolby-product, for example methyl salicylate, at its ester carbonyl groupwith a dihydroxy aromatic compound or a hydroxy group of a growingpolymer chain. Further reaction of the ester-substituted phenolichydroxy group leads to formation of a carbonate linkage. Thus, theester-substituted phenol by-product of reaction of an ester-substituteddiaryl carbonate with a dihydroxy aromatic compound, may be incorporatedinto the main chain of a linear polycarbonate. The presence ofuncontrolled amounts of ester carbonate linkages in the polycarbonatepolymer chain is undesirable.

[0053] Another undesirable structural feature present in meltpolymerization reactions between ester-substituted diaryl carbonates anddihydroxy aromatic compounds is the ester-linked terminal group havingstructure X

[0054] which possesses a free hydroxyl group. Structure X is thought toarise in the same manner as structure IX but without further reaction ofthe ester-substituted phenolic hydroxy group. The presence ofuncontrolled amounts of hydroxy terminated groups such as X isundesirable. In structures VIII, IX and X the wavy line shown as

[0055] represents the product polycarbonate polymer chain structure.

[0056] The present invention, in sharp contrast to known methods ofeffecting the melt polymerization of an ester-substituted diarylcarbonate and a dihydroxy aromatic compound, provides a means oflimiting the formation of internal ester-carbonate linkages havingstructure IX as well as ester-linked terminal groups having structure X,during melt polymerization. Thus in a product polycarbonate preparedusing the method of the present invention structures, IX and X, whenpresent, represents less than 1 mole percent of the total amount of allstructural units present in the product polymer derived from dihydroxyaromatic compounds employed as starting materials for the polymersynthesis.

[0057] An additional advantage of the method of the present inventionover earlier methods of melt polymerization of ester-substituted diarylcarbonates and dihydroxy aromatic compounds, derives from the fact thatthe product polymer is endcapped with ester-substituted phenoxyendgroups and contains very low levels, less than about 50 percent,preferably less than about 10 percent, and still more preferably lessthan about 1 percent, of polymer chain ends bearing free hydroxy groups.The ester substituted terminal groups are sufficiently reactive to allowtheir displacement by other phenols such as p-cumylphenol. Thus,following the melt polymerization the product polycarbonate may betreated with one or more exogenous phenols to afford a polycarbonateincorporating endgroups derived from the exogenous phenol. The reactionof the ester substituted terminal groups with the exogenous phenol maybe carried out in a first formed polymer melt or in a separate step.

[0058] In one embodiment of the present invention an exogenousmonofunctional phenol, for example p-cumylphenol, is added at the outsetof the reaction between the ester substituted diaryl carbonate and thedihydroxy aromatic compound. The product polycarbonate then containsendgroups derived from the exogenous monofunctional phenol. Theexogenous monofunctional phenol serves both to control the molecularweight of the product polycarbonate and to determine the identity of thepolymer endgroups. The exogenous monofunctional phenol may be added inamounts ranging from about 0.1 to about 10 mole percent, preferably fromabout 0.5 to about 8 mole percent and still more preferably from about 1to about 6 mole percent based on the total number of moles ofdihydroxyaromatic compound employed in the polymerization. Additionalcatalyst is not required apart from the catalytically effective amountadded to effect the polymerization reaction. Suitable exogenousmonofunctional phenols are exemplified by p-cumylphenol; 2,6-xylenol;4-t-butylphenol; p-cresol; 1-naphthol; 2-naphthol; cardanol;3,5-di-t-butylphenol, p-nonylphenol; p-octadecylphenol; and phenol. Inalternative embodiments of the present invention the exogenousmonofunctional phenol may be added at an intermediate stage of thepolymerization or after its completion. In such alternative embodimentsthe exogenous phenol may exert a controlling effect upon the molecularweight of the product polycarbonate and will control the identity of thepolymer terminal groups.

[0059] The present invention may be used to prepare polycarbonateproducts having very low levels (less than 1 ppm) of trace contaminantssuch as iron, chloride ion, and sodium ion. Where such extremely lowlevels of trace contaminants is desired it is sufficient to practice theinvention using starting materials, ester-substituted diary carbonateand dihydroxy aromatic compound having correspondingly low levels of thetrace contaminants in question. For example, the preparation bisphenol Apolycarbonate containing less than 1 ppm each of iron, chloride ion andsodium ion may be made by the method of the present invention usingstarting materials bis-methyl salicyl carbonate and bisphenol Acontaining less than 1 ppm iron, chloride ion and sodium ion.

[0060] The method of the present invention can be conducted as a batchor a continuous process. Any desired apparatus can be used for thereaction. The material and the structure of the reactor used in thepresent invention is not particularly limited as long as the reactor hasan ordinary capability of stirring and the presence of adventitiouscatalysts can be controlled. It is preferable that the reactor iscapable of stirring in high viscosity conditions as the viscosity of thereaction system is increased in later stages of the reaction.

[0061] Polycarbonates prepared using the method of the present inventionmay be blended with conventional additives such as heat stabilizers,mold release agents and UV stabilizers and molded into various moldedarticles such as optical disks, optical lenses, automobile lampcomponents and the like. Further, the polycarbonates prepared using themethod of the present invention may be blended with other polymericmaterials, for example, other polycarbonates, polyestercarbonates,polyesters and olefin polymers such as ABS.

EXAMPLES

[0062] The following examples are set forth to provide those of ordinaryskill in the art with a detailed description of how the methods claimedherein are evaluated, and are not intended to limit the scope of whatthe inventors regard as their invention. Unless indicated otherwise,parts are by weight, temperature is in ° C.

[0063] Molecular weights are reported as number average (M_(n)) orweight average (M_(w)) molecular weight and were determined by gelpermeation chromatography (GPC) analysis, using a polycarbonatemolecular weight standard to construct a broad standard calibrationcurve against which polymer molecular weights were determined. Thetemperature of the gel permeation columns was about 25° C. and themobile phase was chloroform.

[0064] Fries content was measured by the KOH methanolysis of resin andis reported as parts per million (ppm). The Fries content for each ofthe melt polycarbonates listed in Table 1 was determined as follows.First, 0.50 grams of polycarbonate was dissolved in 4.0 ml of THF(containing p-terphenyl as internal standard). Next, 3.0 ml of 18% KOHin methanol was added to this solution. The resulting mixture wasstirred for two hours at this temperature. Next, 1.0 ml of acetic acidwas added, and the mixture was stirred for 5 minutes. Potassium acetateby-product was allowed to crystallize over 1 hour. The solid wasfiltered off and the resulting filtrate was analyzed by liquidchromoatograph using p-terphenyl as the internal standard.

[0065] Internal ester-carbonate and terminal hydroxy-ester groups weremeasured by ¹³C- and ³¹P-NMR respectively. Terminal hydroxy ester groupswere first derivatized with 2-chloro-1, 3, 2-dioxaphopholane (Aldrich).

[0066] Melt polymerization reactions were run in a 100 mL glass reactoradapted for distillation under vacuum equipped with a solid nickelhelical agitator. The reactor was configured such that by-product phenolor methyl salicylate could be distilled out of the reaction vessel andcondensed in a chilled receiving vessel. Prior to its use, the reactorwas soaked in 3N HCl for a period of 12 hours and was then soaked for anadditional 12 hours in deionized water (18-Mohm) and placed in a dryingoven overnight. Reaction temperature was controlled by immersion of thereactor into a fluidized sand bath equipped with a PID temperaturecontroller. The temperature of the sand bath was monitored at thereactor sand bath interface. The pressure of the reaction vessel wascontrolled by means of a vacuum pump coupled to a nitrogen bleed. Thepressure within the reactor was measured with an MKS pirani gauge.Sodium hydroxide (J. T. Baker, 1×10⁻⁶ mole per mole bisphenol A) andtetramethyl ammonium hydroxide (Sachem, 2.5×10⁻⁴ mole per mole bisphenolA) or tetrabutyl phosphonium acetate (Sachem, 2.5×10⁻⁴ mole per molebisphenol A) were added as solutions in deionized (18 Mohm) water. Wherethe catalyst level was varied, the concentration of the catalystsolution was adjusted such that the volume of water introduced in thecatalyst introduction step was held constant.

Examples 1-3 and Comparative Examples 1-4

[0067] The reactor was charged at ambient temperature and pressure withsolid bisphenol A (General Electric Plastics Japan Ltd., 0.08761 mol)and solid bis-methyl salicyl carbonate (0.0880-0.0916 mol) or soliddiphenyl carbonate (General Electric Plastics Japan Ltd., 0.0946 mol).In some instances a monofunctional phenol such as p-cumylphenol(0.0027-0.0088 mol) was added in order to limit the molecular weight ofthe polymer and control chain endgroup identity. The catalyst was theninjected into the bisphenol A layer and the reactor was assembled. Thereactor was then evacuated briefly and nitrogen was reintroduced. Thisstep was repeated three times. The reactor was then lowered into thesand bath maintained at 180° C. After a five minute period stirring at250 rpm was initiated. After a total of 10 minutes the reaction mixturehad fully melted. The temperature of the bath was raised to 210° C. overa five minute period. The pressure in the reactor was then reduced to180 mmHg at which point the phenolic by-product began to distill fromthe reaction vessel into the receiving vessel. The reaction mixture washeld at 210° C. and 180 mmHg for 20 minutes. The pressure was thenlowered to 100 mmHg stirred for an additional 20 minutes after whichtime the temperature was raised to 240 ° C. over a five minute period.The pressure was then lowered to 15 mmHg and the reaction mixture wasstirred at 240° C. at 15 mmHg for 20 minutes. The temperature was thenraised to 270° C. over a five minute period and the pressure was thenlowered to 2 mmHg. The reaction mixture was stirred at 270° C. at 2 mmHgfor 10 minutes. The temperature was then raised to 310° C. over a tenminute period and the pressure was lowered to 1.1 mmHg. The reactionmixture was stirred at 310° C. at 1.1 mmHg for 30 minutes after whichthe reaction vessel was raised from the sand bath and the molten productpolymer was scooped from the reaction vessel into a liquid nitrogen bathin order to quench the reaction.

[0068] Data for Examples 1-3 and Comparative Examples 1-5 are gatheredin Table 1 and illustrate the utility of the method of the presentinvention. In the Comparative Examples 1-5 and Examples 1-3 nop-cumylphenol was added as a chainstopper. The column heading “DAC”indicates which diaryl carbonate was employed. “DPC” is diphenylcarbonate used in Comparative-Example 1 (CE-1). “BMSC” is bis-methylsalicyl carbonate. The ratio “DAC/BPA” represents the initial molarratio of diaryl carbonate to bisphenol A employed in the reaction.“M_(n)” represents number average molecular weight of the productpolymer. “Fries level” indicates the concentration of Friesrearrangement product present in the product polymer. Fries levels weredetermined by complete solvolysis (KOH catalyzed methanolysis) of theproduct polymer and quantitative measurement of the amount of Friesproduct, 2-carboxybisphenol A (CAS No. 101949-49-9), present by HPLC.“EC (%)” represents the percentage of polymer chain ends not terminatingin a hydroxyl group. Hydroxyl endgroup concentrations were determined byquantitative infrared spectroscopy. Phenol and salicyl endgroups weredetermined by HPLC analysis after product solvolysis. TABLE 1 REACTIONOF BPA WITH DIARYLCARBONATE (DAC) Example DAC DAC/BPA M_(n) Fries levelEC(%) CE-1 DPC 1.08 6250 946  41% Example 1 BMSC 1.08 4293 notdetected >99% Example 2 BMSC 1.04 8499 not detected >99% Example 3 BMSC1.02 13762 not detected  98% CE-2¹ BMSC 1.04 7683 43 CE-3² BMSC 1.047892 282 CE-4³ BMSC 1.04 gel 8502 CE-5³ BMSC 1.0 5910 98  47%

[0069] Comparative Example 1 highlights differences between meltpolymerization behavior of DPC and BMSC in reactions with bisphenol A.Melt polymerization using BMSC (Example 1) affords an undetectable levelof Fries product and a very high level of endcapping, whereas meltpolymerization using DPC under the same conditions using the samecatalyst as that used in Example 1 leads to a high level (946 ppm) ofFries product and a far lower endcapping level. Examples 1-3 illustratethe melt polymerization of BMSC with BPA according to the method of thepresent invention which affords polycarbonate containing undetectablelevels of Fries product and very high endcapping levels.

[0070] According to the method of the present invention the catalystcomprises at least one source of alkaline earth ions or alkali metalions, and at least one quaternary ammonium compound, quaternaryphosphonium compound or a mixture thereof. Comparative Examples 2 and 3illustrate this requirement. In Comparative Example 2, a source ofalkali metal ions, NaOH, was present but no quaternary ammonium compoundor quaternary phosphonium compound was present. In Comparative Example,3 a quaternary phosphonium compound, tetra butyl phosphonium acetate,was present but no source of alkali metal ions was present. In bothinstances detectable levels of Fries product were observed.

[0071] The data in Table 1 further illustrate the superiority of themethod of the present invention over earlier polymerization methodsusing BMSC. Comparative Examples 4 and 5 show the effect of usinglithium stearate at a level (1×10⁻³ mole per mole BPA) taught by U.S.Pat. No. 4,323,668. Comparative Example 4 was run using the protocolused in Examples 1-3 and the product polycarbonate showed such a highlevel of Fries product that its molecular weight could not be determineddue to the very high level of branching which occurred. The productpolycarbonate was recovered as a gel which could not be dissolved forgel permeation chromatography. Comparative Example 5 was run under amilder temperature regime, the maximum temperature was 260° C. (Seebelow), than that used in Examples 1-3 and Comparative Examples 1-4, yetnonetheless the product polymer contained a significant amount of Friesproduct, 98 ppm.

Comparative Example No. 5 (CE-5, Table 1)

[0072] The reactor, equipped and passivated as described above, wascharged at ambient temperature and pressure with solid bisphenol A(General Electric Plastics Japan Ltd., 0.100 mol) and solid bis-methylsalicyl carbonate (0.100). Lithium stearate catalyst (Kodak, 1×10⁻³ moleper mole bisphenol A) was added as a solid and the reactor wasassembled. The reactor was then evacuated briefly and nitrogen wasreintroduced. The degassing step was repeated three times. The reactorwas then lowered into the sand bath maintained at 150° C. After a fiveminute period stirring at 250 rpm was initiated. These conditions weremaintained for 60 minutes. The temperature of the bath was then raisedto 260° C. The pressure in the reactor was then reduced to 10 mmHg atwhich point the methyl salicylate by-product began to distill from thereaction vessel into the receiving vessel. The reaction mixture was heldat 260° C. and 10 mmHg for 10 minutes after which the reaction vesselwas raised from the sand bath and the molten product polymer was scoopedfrom the reaction vessel into a liquid nitrogen bath in order to quenchthe reaction. The product polycarbonate was characterized by gelpermeation chromatography and found to have M_(w)=14353 M_(n)=5910. Thelevel of Fries product was determined to be 98 ppm.

[0073] As noted, it has been found that the inclusion of an exogenousphenol such as p-cumylphenol in the melt reaction of a bisphenol with anester-substituted diaryl carbonate according to the method of thepresent invention affords polycarbonate containing p-cumylphenolendgroups. Data are gathered in Table 2 which demonstrate the surprisingefficiency of this transformation relative to the analogous reactionusing diphenyl carbonate (DPC). Comparative Example 7 illustrates thelow levels of PCP incorporation in the product polycarbonate encounteredwhen a mixture of a bisphenol, DPC and an endcapping agent,p-cumylphenol (PCP) are reacted in the melt. Conversely, Example 5conducted utilizing the method of the present invention reveals a highlevel of PCP incorporation. In the polycarbonate product formed inComparative Example 7 roughly half of the endgroups were found by NMR tobe derived from PCP and half derived from phenol. TABLE 2 REACTION OFBPA WITH DAC IN THE PRESENCE OF PCP Example DAC DAC/BPA PCP M_(n) EC(%)% PCP CE-6 DPC 1.08 — 6250  41% — CE-7 DPC 1.08 3.05 5674  60% 25%Example 4 BMSC 1.04 — 8499 100% — Example 5 BMSC 1.03 5.07 9744  99% 97%

[0074] The invention has been described in detail with particularreference to preferred embodiments thereof, but it will be understood bythose skilled in the art that variations and modifications can beeffected within the spirit and scope of the invention.

What is claimed is:
 1. A method of preparing polycarbonate comprisingheating a mixture comprising a catalyst, at least one diaryl carbonatehaving structure I

wherein R¹ and R² are independently C₁-C₂₀ alkyl radicals, C₄-C₂₀cycloalkyl radicals or C₄-C₂₀ aromatic radicals, R³ and R⁴ areindependently at each occurrence a halogen atom, cyano group, nitrogroup, C₁-C₂₀ alkyl radical, C₄-C₂₀ cycloalkyl radical, C₄-C₂₀ aromaticradical, C₁-C₂₀ alkoxy radical, C₄-C₂₀ cycloalkoxy radical, C₄-C₂₀aryloxy radical, C₁-C₂₀ alkylthio radical, C₄-C₂₀ cycloalkylthioradical, C₄-C₂₀ arylthio radical, C₁-C₂₀ alkylsulfinyl radical, C₄-C₂₀cycloalkylsulfinyl radical, C₄-C₂₀ arylsulfinyl radical, C₁-C₂₀alkylsulfonyl radical, C₄-C₂₀ cycloalkylsulfonyl radical, C₄-C₂₀arylsulfonyl radical, C₁-C₂₀ alkoxycarbonyl radical, C₄-C₂₀cycloalkoxycarbonyl radical, C₄-C₂₀ aryloxycarbonyl radical, C₂ -C₆₀alkylamino radical, C₆-C₆₀ cycloalkylamino radical, C₅-C₆₀ arylaminoradical, C₁-C₄₀ alkylaminocarbonyl radical, C₄-C₄₀cycloalkylaminocarbonyl radical, C₄-C₄₀ arylaminocarbonyl radical, andC₁-C₂₀ acylamino radical; and b and c are independently integers 0-4;and at least one dihydroxy aromatic compound, said catalyst comprisingat least one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compoundor a mixture thereof, said source of alkaline earth ions or alkali metalions being present in an amount such that between about 10⁻⁵ and about10⁻⁸ moles of alkaline earth metal ions or alkali metal ions are presentin the mixture per mole of dihydroxy aromatic compound employed, saidquaternary ammonium compound, quaternary phosphonium compound or mixturethereof being present in an amount between about 2.5×10⁻³ and about1×10⁻⁶ moles per mole of dihydroxy aromatic compound employed.
 2. Amethod according to claim 1 wherein said dihydroxy aromatic compoundselected from the group consisting of bisphenols having structure II,

wherein R⁵-R¹² are independently a hydrogen atom, halogen atom, nitrogroup, cyano group, C₁₋C₂₀ alkyl radical C₄₋C₂₀ cycloalkyl radical, orC₆₋C₂₀ aryl radical; W is a bond, an oxygen atom, a sulfur atom, a SO₂group, a C₆-C₂₀ aromatic radical, a C₆-C₂₀ cycloaliphatic radical or thegroup

wherein R¹³ and R¹⁴ are independently a hydrogen atom, C₁₋C₂₀ alkylradical, C₄₋C₂₀ cycloalkyl radical, or C₄₋C₂₀ aryl radical; or R¹³ andR¹⁴ together form a C₄₋C₂₀ cycloaliphatic ring which is optionallysubstituted by one or more C₁₋C₂₀ alkyl, C₆₋C₂₀ aryl, C₅₋C₂₁ aralkyl,C₅₋C₂₀ cycloalkyl groups or a combination thereof; dihydroxy benzeneshaving structure III

wherein R¹⁵ is independently at each occurrence a halogen atom, nitrogroup, cyano group, C₁₋C₂₀ alkyl radical, C₄₋C₂₀ cycloalkyl radicalC₄₋C₂₀ aryl radical; and d is an integer from 0 to 4; and dihydroxynaphthalenes having structures IV and V

wherein R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently at each occurrence ahalogen atom, nitro group, cyano group, C₁₋C₂₀ alkyl radical, C₄₋C₂₀cycloalkyl radical C₄₋C₂₀ aryl radical; e and f are integers of from 0to 3, g is an integer from 0 to 4, and h is an integer from 0 to
 2. 3. Amethod according to claim 1 wherein said quaternary ammonium compoundcomprises structure VI

wherein R²⁰-R²³ are independently a C₁₋C₂₀ alkyl radical, C₄₋C₂₀cycloalkyl radical or a C₄₋C₂₀ aryl radical and X⁻ is an organic orinorganic anion.
 4. A method according to claim 3 wherein R²⁰-R²³ areindependently C₁-C₅ alkyl.
 5. A method according to claim 4 whereinR²⁰-R²³ are each methyl radicals.
 6. A method according to claim 2wherein said anion is selected from the group consisting of hydroxide,halide, carboxylate, sulfonate, sulfate, carbonate, and bicarbonate. 7.A method according to claim 1 wherein said quaternary ammonium compoundis tetramethyl ammonium hydroxide.
 8. A method according to claim 1wherein said phosphonium compound comprises structure VII

wherein R²⁴-R²⁷ are independently a C₁₋C₂₀ alkyl radical, C₄₋C₂₀cycloalkyl radical or a C₄₋C₂₀ aryl radical and X⁻ is an organic orinorganic anion.
 9. A method according to claim 8 wherein R²⁴-R²⁷ areindependently C₁-C₅ alkyl.
 10. A method according to claim 9 whereinR²⁴-R²⁷ are each methyl radicals.
 11. A method according to claim 8wherein said anion is selected from the group consisting of hydroxide,halide, carboxylate, sulfonate, sulfate, carbonate, and bicarbonate. 12.A method according to claim 1 wherein said quaternary phosphoniumcompound is tetrabutyl phosphonium hydroxide.
 13. A method according toclaim 1 wherein said source of alkaline earth or alkali metal ions is analkali metal hydroxide, an alkaline earth metal hydroxide or a mixturethereof.
 14. A method according to claim 13 wherein said alkali metalhydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide ora mixture thereof.
 15. A method according to claim 1 wherein said sourceof alkaline earth or alkali metal ions is a salt of EDTA.
 16. A methodaccording to claim 15 wherein said salt of EDTA is EDTA magnesiumdisodium salt.
 17. A method according to claim 1 wherein said mixture isheated to a temperature in a range between about 100° C. and about 340°C.
 18. A method according to claim 17 wherein said mixture is heated toa temperature in a range between about 100° C. and about 280° C.
 19. Amethod according to claim 18 wherein said mixture is heated to atemperature in a range between about 140° C. and about 240° C.
 20. Amethod according to claim 1 wherein said mixture is heated at subambientpressure.
 21. A method according to claim 20 wherein said pressure is ina range between about 0.00001 and about 0.9 atmospheres.
 22. A methodaccording to claim 1 wherein said mixture is heated at ambient orsuprambient pressure.
 23. A method according to claim 22 wherein saidpressure is in a range between about 1 and about 2 atmospheres.
 24. Amethod according to claim 1 wherein diaryl carbonate 1 is bis-methylsalicyl carbonate.
 25. A method according to claim 24 wherein the endgroups are derived from methyl salicylate.
 26. A method according toclaim 2 wherein bisphenol II is selected from the group consisting of2,2-bis(4-hydroxyphenyl)propane (bisphenol-A);bis(4-hydroxy-3-methylphenyl)cyclohexane;2,2-bis(4-hydroxy-3-methylphenyl)propane; bis(4-hydroxyphenyl)methane;1,1-bis(4-hydroxyphenyl)ethane;; 2,2-bis(4-hydroxyphenyl)butane;2,2-bis(4-hydroxyphenyl)octane;2,2-bis(4-hydroxy-3-tert-butylphenyl)propane;1,1-bis(4-hydroxy-3-sec-butylphenyl) propane;2,2-bis(4-hydroxy-3-bromophenyl)propane;1,1-bis(4-hydroxyphenyl)cyclopentane;1,1-bis(4-hydroxyphenyl)cyclohexane; and 4,4′-dihydroxydiphenyl ether.27. A method according to claim 26 wherein bisphenol II is bisphenol A.28. A method according to claim 1, said mixture further comprising atleast one exogenous monofunctional phenol.
 29. A method according toclaim 28 wherein said polycarbonate comprises endgroups derived from anexogenous monofunctional phenol.
 30. A method according to claim 29wherein said end groups are derived from said monofunctional phenolsselected from the group consisting of 2,6-xylenol, p-t-butylphenol,p-cresol, cardanol, p-cumylphenol, p-nonylphenol, p-octadecylphenol,1-naphthol, and 2-naphthol.
 31. A method according to claim 1 whereinsaid dihydroxy aromatic compound contains less than 1.0 parts permillion each of sodium ion, iron and chloride.
 32. A method according toclaim 1 wherein said polycarbonate contains less than 1.0 parts permillion each of sodium ion, iron and chloride.
 33. A molded articleprepared from the polycarbonate made by the method of claim
 32. 34. Amethod of preparing bisphenol A polycarbonate comprising heating amixture of bisphenol A with from about 0.8 to about 1.10 molarequivalents of bis-methyl salicyl carbonate at a temperature in a rangebetween about 140° C. and about 240° C., and a pressure in a rangebetween about 0.01 mmHg and about 760 mmHg, in the presence of acatalyst comprising sodium hydroxide and a quaternary ammonium compoundor quaternary phosphonium compound, said sodium hydroxide being presentin an amount in a range between about 1×10⁻⁵ and about 1×10⁻⁸ molessodium hydroxide per mole starting bisphenol A, said quaternary ammoniumcompound or quaternary phosphonium compound being present in an amountbetween about 2.5×10⁻³ and about. 2.5×10⁻⁶ moles per mole startingbisphenol A.
 35. A method according to claim 34 wherein the quaternaryammonium compound is tetramethyl ammonium hydroxide.
 36. A methodaccording to claim 34 wherein the quaternary phosphonium compound istetrabutyl phosphonium acetate.
 37. A method of preparing bisphenol Apolycarbonate comprising heating a mixture of bisphenol A with fromabout 0.8 to about 1.10 molar equivalents, based on moles of bisphenolA, of bis-methyl salicyl carbonate, and about 0.1 mole percent to 10mole percent based upon the number of moles of bisphenol A employed, ofa monofunctional phenol, at a temperature in a range between about 140°C. and about 240° C., and a pressure in a range between about 0.01 mmHgand about 760 mmHg, in the presence of a catalyst comprising sodiumhydroxide and a quaternary ammonium compound or quaternary phosphoniumcompound, said sodium hydroxide being present in an amount in a rangebetween about 1×10⁻⁵ and about 1×10⁻⁸ moles sodium hydroxide per molestarting bisphenol A, said quaternary ammonium compound or quaternaryphosphonium compound being present in an amount between about 2.5×10⁻³and about. 2.5×10⁻⁶ moles per mole starting bisphenol A.
 38. A methodaccording to claim 35 in which the monofunctional phenol is selectedfrom the group comprising 2,6-xylenol, p-t-butylphenol, p-cresol,cardanol, p-cumylphenol, p-nonylphenol, p-octadecylphenol, 1-naphthol,and 2-naphthol.